A key is a set of notes that a piece of music revolves around. If a song is in a certain key, that means that every note in that key will "work" with that song. Otherwise, if you play in a different key to the one the song is in, there may be some notes that sound like they don't harmonize well.
Different keys are made up of many different notes. Some notes may overlap with other keys, but what differentiates them is their tonal center.
All keys have a tonal center which is basically a note that the key focuses on or revolves around. We can also think of this note as our root note from our previous lessons.
Another way to think about a key is by the scale that the song uses. For example, if we say a song is in the key of C Major, this means that we can use the C Major scale to play along with the song.
To demonstrate, let's take a look at Blink 182's "Dammit", a song in the key of C Major:
Because the song is in C Major, we're able to use any of the notes from that scale (C, D, E, F, G, A, B, C). Let's look at the main riff as an example:
As you can see, each one of the notes for this riff is part of the C Major scale! Essentially, they could have created a melody using any one of these notes. However, any note outside of this key/scale would probably sound discordant.
You may have also noticed that the notes for this riff look familiar. Remember major scale box pattern one?
This riff is basically just part of the bottom portion of the box pattern. From this, we can also see that the tonal center, or root note, is C. The key of C Major revolves around this note.
Finding out the key for a song can be a bit of a challenge. In the end, it requires a bit of detective skills because there is no concrete formula for doing this. There are, however, some methods/guidelines that can help:
If you know the root note, you can build any type of scale off of it and see if the notes in the song match that scale.
To help find the root note:
Another way is by analyzing the notes within each chord or riff and seeing which scale those notes create. Let's use the verse from "Dammit" to see how we can do this:
We see that these chords have the notes: C, D, E, F, G, A. They're missing the "B" that's in the C Major scale, but we have all the other notes in the scale, so that should tell us there's a pretty high chance that the song is in C Major (and it is).
Alternatively, you can also use chord scale theory to help figure this out. We'll be covering this later since it's a pretty hefty and important concept that warrants its own dedicated lesson.
Nice job on learning about keys! We're getting closer and closer to learning all the tools necessary to be able to improvise. But before that, let's learn about and memorize the most used scale for Rock guitarists, the pentatonic scale.
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